Electrochemically Synthesized Electrochemically Synthesized

Sungho Park

SungKyunKwan University, Department of Chemistry &

SKKU Advanced Institute of Nanotechnology (SAINT)

Electrochemically Synthesized Electrochemically Synthesized

Multi

Multi - - block block Nanorods Nanorods

J. Am. Chem. Soc. 2003, 125, 2282-2290 Electrochim. Acta. 2002, 47, 3611-3620 J. Phys. Chem. B 2002, 106, 8667-8670 Langmuir 2002, 18, 5792-5798

J. Am. Chem. Soc. 2002, 124 (11), 2428-2429 Langmuir 2002, 18, 3233-3240

J. Phys. Chem. B 2001, 105, 9719-9725 Electrochem. Comm. 2001, 3, 509-513 J. Phys. Chem. B 2000, 104, 8250-8258

Electrochemical Vibrational Characterization of Metal Nanoelectrodes

Surface Chemistry Electrochemistry

Nanoparticle electrocatalysis

J. Am. Chem. Soc. 2006, ASAP

J. Phys. Chem. B 2006, 110, 2150-2154 Science, 2005, 309, 113-115

J. Am. Chem. Soc. 2005, 127, 5312-5313 Advanced Materials 2005, 17, 1027-1031 J. Am. Chem. Soc. 2004, 126, 11772-11773 Angew. Chem. Int. Ed.2004, 43, 3048-3050 Science, 2004, 303, 348-351

Nanoparticle Synthesis and Applications

Nanorods

Core-Shell nanoparticles DPN,

Nano-Bio Chemistry

Nanotechnology: What is it?

2. Determining the chemical and physical consequences of miniaturization.

3. Exploiting the ability to miniaturize and its consequences in the development of new technology.

1. Developing synthetic and analytical tools for

characterizing and manipulating materials on the

nanometer (nm) length scale.

Nanometer Scale Materials

Why are we interested in small particles?

Single particle &

Atomic species Bulk species

Many fascinating potential uses: quantum dots or quantum

computers and devices, chemical sensor, light-emitting diodes, industrial lithography and so on ………Electrochemical catalysts, SERS

Stability of Particles?

Kinetically stable, not thermodynamically Energy

Particle Size n=309 n=147

n=55

Bulk metal

(a) (b)

+ ++ + + + – – –

– – – – –

– + ++ +

+ +

– –

– – – – –

–

(by K. Kinoshita)

Carbon Supported Nanoparticles

-0.2 0.0 0.2 0.4 0.6 10 ^μA

b'

b

a a'

Potential (V vs SCE)

Underpotential Deposition of Copper Monolayer

Cu²⁺ + 2e^-_substrate Cu⁰_UPD

Au

Cu

+ Pt

→ Cu

+ Pt

+ 2e^- - 2e^-

Au

+ 2e^- - 2e^-

Replacement of Cu

Adlayer with Pt

Au

PtCl₄^2-/Pt E⁰ = 0.48 V Cu²⁺/Cu_upd E⁰ = 0.2 V Pt²⁺

Pt²⁺

Pt²⁺

Pt²⁺

Pt²⁺

Pt²⁺

Pt²⁺

Cu²⁺

Cu²⁺

Cu²⁺

Cu²⁺

Cu²⁺ Cu²⁺

Cu Pt

Pt

Pt-group metal coated gold nanoparticles

OH OH OH OH OH OH OHOH

ITO coated glass

NH₂ NH₂ NH₂ NH₂NH₂ NH₂

Si CH₃0

Au

CH₃0

CH₃0 NH₂

Silanization

NH₂

Cu overlayers

UPD

Au Au

Au Au Au Au Au Au

Metal Exchange

Au Au Au

Cu ²⁺

Pd ²⁺ or Pt ²⁺

SERS of Pt-group modified gold nanoparticles

0.0 0.5 1.0

E/V vs. SCE

0.0 0.5 1.0

E / V vs. SCE

Pt coating Pd coating

2000 1500 1000 500

Relative Intensity

*

*

*

*

2500 cps

1504

1540 1278

1224 2073 350

1969 2080 478

Raman Shift (cm^-1) SERS

Pt / CO

Pd / CO

Pt / C₂H₄ Au / C₂H₄

100 uA/cm² 100 uA/cm²

JACS. 2002, 124(11), 2428 J. Phy. Chem. B 2002, 106, 8667

Nanorod Synthesis

Alumina membrane

150 ~200 nm Ag evaporation

Ag deposition (EC)

Au deposition (EC)

1. HNO₃ 2. NaOH Top view

Side view

working electrode Pt Ag/AgCl

Pioneered by Prof. Martin and Prof. Moskovits

Gold Nanorods

Optical Microscope Images

5 μm 5 μm

Rods made from Conducting Polymers

Charge/C

Length/µm

Polymer Au

0 1 2 3 4 5 6

0 1 2 3 4

Polymer

Au

N H

N H

N H

N H

5 μm

Nanoresistors & Nanodiodes

Resistors

Schottky or P-N Diodes Au Deposition

Low Work Function Metal or Semiconductor Deposition

=

=

Layer by Layer Assembly

Ref. JPCB. 2001, 105, 8762 by T. E. Mallouk et. al.

Electrical Transport Measurement

Electrical Transport Measurement

289K 200K

175K

150K 120K

At Room Temperature, conductivity ~ 3 mS cm^-1

log σ(T) vs 1/T, showing a linear response (σ = σ₀exp(−E_a/kT),

σ: conductivity, T: temperature) the activation energy E_a ~ 0.07 eV.

Au-Ppy-Cd-Au, Schottky Diodes

A E

Reverse Bias

B

D

150 nm

C

Au Cd

PpyAu

Conclusions (Part 2)

• The electrochemical deposition provides

excellent control over the block length of the metal and organic regions of nanorods.

• They show either resistor or diode properties depending on their compositions and spatial distribution of the different compositional

blocks.

Nano-Gap Fabrication

On-Wire Lithography (OWL)

Etching

Deposition of Au/Ti or SiO₂

Sonication 1. Removal of

templates 2. Dispersion of

wires

+

Zoomed-in SEM Images of Wires

5 nm

Lowest limit ~ 5 nm (at current stage)

Zoomed-in Image with Au/Ti coating, after chemical etching of Ag blocks.

25 nm 50 nm 100 nm

Photo-Sensitive DPN Patterns at the Gap

-1.0 -0.5 0.0 0.5 1.0

-2.0x10^-9 -1.5x10^-9 -1.0x10^-9 -5.0x10^-10 0.0 5.0x10^-10 1.0x10^-9 1.5x10^-9 2.0x10^-9

Current / A

Potential / V

Au-Gap (13nm)-Au, DPN of PEO:Ppy

= 1:1 (w/w %)

Xe Light Exposure

SEM Image of wire on micorelectrodes after DPN of a mixture of PEO & Ppy

Scanned starting from –1.0 V to +1.0 V, Xe Light was shined on the gap

at –0.1 V on the way back

Without polymer

With polymer

SEM Image and EDS of Disk Arrays

40 nm

SEM Images of Nano-Disk Arrays after Si Deposition

EDS of Nano-Disk Arrays

after Si Deposition and Ag Etching

Si

Au

Conclusions (Part 3)

• The electrochemical deposition and selective etching provide excellent control over metal block length and nano gap distance in

nanorods.

• They show potential application in molecular electronics and we demonstated “proof-of- concenpt” experiment with and without

conducting polymer at the gap.

Multicomponent Magnetic Nanorods for

Biomolecular Separations

Affinity of Poly-His to Ni Blocks of Au- Ni-Au Nanorods

~ 4 × 10

Nanorods

A B

A B

Multicomponent Magnetic Nanorods for Biomolecular Separations

5 μm 5 μm

A B

C D

Anti-PolyHis Ig G Antibody

Separation by Au-Ni-Au Nanorods

Multi-Component Separation

A B C D

A

B

Selective binding

C D

Magnetic separation His-tagged protein release

Biotin-tagged protein release

Biotin tagged protein (BSA)

Histidine tagged protein (ubiquitin) Nitrostreptavidin

nontagged protein (protein A) Dye color

Conclusions (Part 4)

ƒ Multicomponent metal nanorods have several advantages (e.g. stability and modification).

ƒ Multiblock nanorods can be used for separation of various proteins by exploiting the chemical and

physical properties of these nanostructures.

ƒ The nanorods provide increased surface area and are a pseudo-homogeneous system, increasing the

efficiency of the target binding and separation

process.

Acknowledgements

Purdue University (West Lafayette), Prof. Michael J. Weaver

Acknowledgements

NSF AFOSR

DARPA

NIH ONR

Northwestern University, Prof. Chad A. Mirkin